This is a study of the metabolism of infused and endogenous foods and fuels under normal control conditions in fasting man, under traumatized conditions in the human patient, and in the squirrel monkey. The objectives are to discern the activity of various substrates in promoting protein synthesis under a variety of conditions, to examine this not only by metabolic balance, but by the metabolism of N15 glycine used as an infused tracer substance, and to examine these phenomena in the circadian rhythm acclimatized and synchronized squirrel monkey. In normal human volunteer subjects, a variety of infused intravenous substrates are given together with tracer amounts of N15 glycine. Intentional perturbation of these equilibrium curves is produced by exercise, by diet change and by the interference with protein synthesis accompanying cancer chemotherapy. In patients of a variety of types, including trauma, elective surgery and cancer under chemotherapy, similar observations are being made. Finally, the squirrel monkey preparation as adapted in our Department of Physiology is used to examine the impact of circadian rhythms on the metabolism of infusions of nutritious substrates such as amino acids, glucose and fat. Our purpose here is to examine the impact of daily rhythms on the ability to synthesize protein from infused substances.